The invention relates to a method and a system for automatically injecting chemicals into a pressurized system.
In various industries such as the petroleum industry, fluids or chemicals often need to be introduced into pressurized systems including pipelines and other apparatus for various purposes. In particular, it is often necessary to introduce alcohols such as monohydric aliphatic alcohols (for example, methanol) or secondary butyl alcohol into pressurized pipelines to prevent pipeline freeze-up in cold regions.
At the present time in the petroleum industry, reciprocating diaphragm pumps driven by a gas are generally used for injecting chemicals into pipelines. The pumps, by virtue of their reciprocating action, use large volumes of gas to drive the diaphragms. While effective in injecting the desired chemical into the pipeline, the primary drawback of these systems is that ultimately pump gas is vented into the atmosphere on each pump stroke. Pump gas is both harmful to the atmosphere and expensive to operate. Accordingly, there has been a need in the petroleum industry for an injection system which does not vent large quantities of gas to the atmosphere with the attendant benefits of reducing the requirements for high volume pressure equipment and the associated operational costs.
U.S. Pat. No. 2,266,981 (Miller) discloses a method and apparatus for injecting chemicals into a natural gas pipeline for inhibiting the formation of solid gas hydrate within the pipeline in cold temperatures. The apparatus teaches a fluid supply tank for storing the chemical to be injected, a pressure feed tank for pressurizing and injecting the chemical into the pipeline and a series of lines, manual valves and gauges for controlling the flow of chemicals from the supply tank into the feed tank and ultimately into the pipeline using gravity. However, while this system may be effective in injecting chemicals into a pipeline, the system requires manual operation of the valves as well as constant monitoring to ensure that a continuous and regulated amount of chemical is supplied to the pipeline.
Further, some chemical injection systems in industries other than the petroleum industry also provide elements similar to U.S. Pat. No. 2,266,981. For instance, U.S. Pat. No. 2,935,391 (Evans) and U.S. Pat. No. 611,871 (Sumner) generally teach apparatus for adding a chemical to a product and include a supply drum, a pressure vessel and a series of manual valves and gauges for controlling the flow of chemical through the apparatus into the product. The apparatus taught by each of these references requires manual operation of the valves and constant monitoring to ensure a continuous amount of chemical is supplied in consistent quantities to the pipeline.
Accordingly, there has been a need for an injection system which automates the injection of chemicals into pressurized systems without the problems associated with the prior art.
An object of the present invention is to provide an injection method and system for automatically controlling valve operation and automatically controlling the quantity of chemical injected into a pressurized system. With particular regard to the petroleum industry, a further object of the present system is to reduce the quantity of pumping gas and eliminate the need for a high volume pressure vessel while, by virtue of the system, eliminate the need for a pump.
In one embodiment, the invention provides a system for introducing a chemical into a pressurized system comprising:
a low pressure storage tank for storing a volume of chemical at a low pressure;
a high pressure storage vessel in fluid communication with the low pressure storage tank and the pressurized system; and
a control system in operative communication with the high pressure storage vessel for automatically equalizing the pressure between the low pressure storage tank and the high pressure storage vessel, for automatically equalizing the pressure between the high pressure storage vessel and the pressurized system and for controlling the flow of chemical through the system.
In a further embodiment, the control system includes a micro-controller having a level sensor within the high pressure storage vessel for detecting the level of chemical in the high pressure storage vessel. The control system may also include at least one vent valve operatively connected to the high pressure storage vessel for venting the pressure of the high pressure storage vessel and at least one pressure valve operatively connected to the high pressure storage vessel for opening to a pressure equalization line operatively connected to the pressurized system for equalizing the pressure of the high pressure storage vessel with the pressure of the pressurized system.
In a still further embodiment, the system includes either a control valve or a check valve operatively connected to a flow line between the low pressure storage tank and the high pressure storage vessel to prevent chemical from flowing back into the low pressure storage tank once the high pressure storage vessel is pressurized. A control valve or check valve may also be operatively connected to a flow line between the high pressure storage vessel and the pressurized system to prevent chemical from flowing back into the high pressure storage vessel when the high pressure storage vessel is being depressurized. If a control valve is used then it is operatively connected and controlled by the control system.
In other embodiments the system includes a rate gauge for determining the rate of chemical injection into the pressurized system, a weir for restricting the flow of chemical within the high pressure storage vessel and other useful features which enhance the utility of the system as will become apparent in the discussion below.
The invention also provides a method for automatically introducing a chemical into a pressurized system comprising:
filling a low pressure storage tank with chemical;
equalizing the pressure of a high pressure storage vessel to the pressure of the low pressure storage tank;
filling the high pressure storage vessel with chemical from the low pressure storage tank;
equalizing the pressure of the high pressure storage vessel to the pressure of the pressurized system; and
injecting chemical into the pressurized system from the high pressure storage vessel wherein the pressure of the high pressure storage vessel and the flow of chemical from the low pressure storage tank to the high pressure storage vessel and from the high pressure storage vessel into the pressurized system is automatically controlled by a control system.